Sharing resources in a system for testing semiconductor devices

ABSTRACT

Probes in a plurality of DUT probe groups can be connected in parallel to a single tester channel. In one aspect, digital potentiometers can be used to effectively switch the tester channel from a probe in one DUT probe group to a probe in another DUT probe group. In another aspect, switches in parallel with a resistor can accomplish such switching. In yet another aspect, a chip select terminal on each DUT can be used to effectively connect and disconnect internal DUT circuitry to the tester channel. Multiple DUT probe groups so connected can be used to create different patterns of DUT probe groups for testing different patterns of DUTs and thus facilitate sharing tester channels.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/566,179 filed Dec. 1, 2006.

BACKGROUND

Semiconductor devices, such as microprocessors, dynamic random accessmemory (DRAM), and flash memory, are fabricated in a known manner on asemiconductor wafer. Depending upon the size of the wafer and of eachdevice formed thereon, there may be as many as several hundred deviceson a single wafer. These devices are typically identical to one another,each including a plurality of conductive terminals on the surfacethereof for power and other connections to the devices such as inputsignals, output signals, control signals and the like.

Oftentimes, it is desirable to test the devices on the wafer todetermine which are functional and which are inoperative or partiallyfunctional. To this end, wafer testers apply power and input signals tothe devices and monitor outputs during a predetermined testing routinewhile the devices are still on the wafer.

Because each DUT is substantially identical to the others, there can bea plurality of identical DUT probe groups. Each DUT probe group includesprobes that make discrete pressure connections to separate ones of theterminals on a corresponding DUT.

These DUT probe groups can be attached to a substrate. This substrateand the probes in the DUT probe groups together form a probe head thatis part of the tester system. The wafer tester typically includesmultiple channels, one for each probe in the DUT probe groups on theprobe head. As a result, multiple DUT probe groups simultaneouslycontact multiple DUTs on the wafer.

Obviously, the more DUTs that can be simultaneously tested, the fasterthe entire wafer can be tested. But there is a limit to the number oftester channels that can be connected to the DUT probe groups. Whilesome testers contain many channels, e.g., 128 channels, there may beseveral hundred DUTs on the wafer to be tested. The testing processconsequently includes bringing the DUT probe groups and terminals on afirst corresponding set of DUTs into contact with one another,performing the test, lifting the probes from the DUTs, moving the probesand wafer relative to one another, bringing the probes into contact withterminals on another set of DUTs, and testing additional DUTs. Thisprocess is repeated until all the DUTs on the wafer are tested.

Efficiency is increased if a probe head having more probes in DUT probegroups than there are tester channels is used in a manner that permitsrapid and effective switching of tester channels from probes in onegroup of DUT probe groups to probes in another DUT probe group. This caneffectively reshape the number and pattern of operational DUT probegroups on the probe head.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a somewhat schematic view of a probe card assembly including aprobe head mounted thereon according to some embodiments of theinvention.

FIG. 2 is a significantly enlarged view of a portion of a DUT probegroup on the probe head of FIG. 1.

FIG. 3 is a schematic depiction of a configuration of DUT probe groupson a probe head according to some embodiments of the invention.

FIG. 4 shows the probe head of FIG. 3 during a first touchdown on awafer having a plurality of DUTs, each being represented schematicallyby a square within a bold line that represents the perimeter of the DUTson the wafer.

FIG. 5 is a view similar to FIG. 4 showing the probe head during asecond touchdown.

FIG. 6 shows another probe head constructed according to someembodiments of the invention during a first touchdown on a wafer havinga plurality of DUTs, each being represented schematically by a squarewithin a bold line that represents the perimeter of the DUTs on thewafer.

FIG. 7 is a view similar to FIG. 6 showing the probe head during asecond touchdown.

FIG. 8 is a highly schematic view of a portion of a circuit constructedin accordance with some embodiments of the invention.

FIG. 9 is a highly schematic view of a portion of a circuit constructedin accordance with some embodiments of the invention.

FIG. 10 is a highly schematic view of a portion of a circuit constructedin accordance with some embodiments of the invention and of DUTsdesigned to operate with this circuit.

FIG. 11 is a highly schematic view of a portion of a circuit constructedin accordance with some embodiments of the invention and of DUTsdesigned to operate with this circuit.

The figures presented in conjunction with this description are views ofonly particular—rather than complete—portions of the devices and methodsof making the devices. Together with the following description, thefigures demonstrate and explain the principles of such devices andmethods according to some embodiments of the invention. In the figures,the thickness of layers and regions may be exaggerated in some instancesfor clarity. It will also be understood that when a layer is referred toas being “on” another layer or substrate, it can be directly on theother layer or substrate, or intervening layers may also be present. Thesame reference numerals in different drawings represent the sameelement, and thus their descriptions will be omitted.

DETAILED DESCRIPTION OF EXEMPLARY EMODIMENTS

This specification describes exemplary embodiments and applications ofthe invention. The invention, however, is not limited to these exemplaryembodiments and applications or to the manner in which the exemplaryembodiments and applications operate or are described herein.

In general, some embodiments of the invention provide ways to connectchannels on a tester to different probes on a probe card assembly. Forexample, during testing of DUTs on a semiconductor wafer, a first set oftester channels could be connected to a first set of probe groups on theprobe card assembly during a first touchdown that makes pressureconnections between terminals on some of the DUTs and the connectedprobe groups. Either while the pressure connection is maintained orafter it is removed, e.g., between the first and a second touchdown, atleast some of the first set of tester channels can be switched to adifferent set of DUT probe groups on the probe card assembly for furthertesting of the DUTs. This switching can be accomplished in various ways,e.g., with digital potentiometers, with a chip select port on each DUTthat could be selected using a signal on one of the probes, or inresponse to the pressure generated by the touchdown. In addition, duringa single touchdown, a single channel may be used to drive a plurality ofprobes, which can be pressure connected to different DUTs.

A non-limiting exemplary probe card assembly 100 (which can be anon-limiting example of a contactor device) illustrated in FIG. 1 can beused to test one or more DUTs in accordance with some embodiments of theinvention. DUTs can be any electronic device or devices to be tested.Non-limiting examples of DUTs include one or more dies of anunsingulated semiconductor wafer, one or more semiconductor diessingulated from a wafer (packaged or unpackaged), an array of singulatedsemiconductor dies disposed in a carrier or other holding device, one ormore multi-die electronics modules, one or more printed circuit boards,or any other type of electronic device or devices. Note that the termDUT, as used herein, refers to one or a plurality of such electronicdevices.

Probe card assembly 100 can include electrical connectors 104, which canmake electrical connections with a plurality of tester channels (notshown) from the tester (not shown). A tester (not shown) can comprise acomputer or computers and/or other electronic elements configured tocontrol testing of DUTs. For example, a tester can generate patterns oftest signals that are to be input into the DUTs, and the tester canevaluate response signals produced by the DUTs in response to the testsignals to determine whether the response signals are as expected and,consequently, whether the DUTs passed the testing. (As used herein, theterm “test signals” can refer to the signals input into the DUTs and/orto the response signals generated by the DUTs.) Communications channels(not shown) (e.g., coaxial cables, fiber optic links, wirelesstransmitters/receives, drivers, receivers, etc. or any combination ofthe foregoing) can be provided to and from the tester. A communicationchannel can be provided for each input and output of a DUT that is to betested. Power, ground, and input signals for testing a DUT can beprovided from the tester through ones of the communications channels,and response signals generated by a DUT can be provided to the testerthrough other communication channels. As will be seen, probe cardassembly 100 can include electrical connectors 104 having individualconnections to the channels from the tester, and the probe card assemblycan also include electrically conductive paths between the channelconnections of the electrical connectors 104 and probes 106 configuredto be pressed against and thus make electrical connections with inputand/or output terminals 108 of a DUT 110 (for example), which arenon-limiting examples of contacts. The probe card assembly 100 can thusprovide an electrical interface between communications channels from thetester and input and/or output terminals 108 of DUTs 110.

As shown in FIG. 1, probe card assembly 100 can comprise one or moresubstrates configured to support connectors 104 and probes 106 andprovide electrical connections between connectors 104 and probes 106.The exemplary probe card assembly 100 shown in FIG. 1 has three suchsubstrates, although in other implementations, probe card assembly 100can have more or fewer substrates. Shown in FIG. 1 are a wiringsubstrate 112, which may be a probe card, an interposer substrate 114,and a probe substrate 116. Wiring substrate 112, interpose substrate114, and probe substrate 116 can be made of any type of material.Examples of suitable substrates include without limitation printedcircuit board, a ceramic substrate, an organic or inorganic substrate,etc. Combinations of the foregoing are also possible. Probe substrate116 with probes 106 can be or can be part of a probe head.

Electrically conductive connections (not visible) can be provided fromconnectors 104 through wiring substrate 112 to electrically conductivespring interconnect structures 118. Other electrically conductiveconnections (not visible) can be provided from spring interconnectstructures 118 through interposer substrate 114 to electricallyconductive spring interconnect structures 120, and still otherelectrically conductive connections (not visible) can be provided fromspring interconnect structures 120 through probe substrate 116 to probes106. The electrical connections (not shown) through the wiring substrate112, interposer substrate 114, and probe substrate 116 can compriseelectrically conductive vias, traces, etc. on, within, and/or throughwiring substrate 112, interposer substrate 114, and probe substrate 116.The electrical connections (not shown) through the wiring substrate 112,the electrically conductive spring structures 118, the electricalconnections (not shown) through the interposer substrate 114, springstructures 120, and the electrical connections (not shown) through theprobe substrate 116 can form a plurality of electrically conductivepaths electrically connecting individual channel connections inelectrical connectors 104 with individual probes 106. There can be aone-to-one correspondence between individual channel connections in theelectrical connectors 104 and the probes 106. Alternatively or inaddition, ones or all of the electrical paths (not shown) from theelectrical connectors 104 to the probes can electrically connect onechannel connection in the electrical connectors 104 with more than oneprobe 106.

Wiring substrate 112, interposer substrate 114, and probe substrate 116can be held together by brackets 122 and/or other suitable means. Theconfiguration of probe card assembly 100 shown in FIG. 1 is exemplaryonly and is simplified for ease of illustration and discussion. Manyvariations, modifications, and additions are possible. For example, aprobe card assembly 100 can have fewer or more substrates (e.g., 112,114, 116) than the probe card assembly 100 shown in FIG. 1. As anotherexample, the probe card assembly 100 can have more than one probesubstrate (e.g., 116), and each such probe substrate can beindependently adjustable. Non-limiting examples of probe card assemblieswith multiple probe substrates are disclosed in U.S. patent applicationSer. No. 11/165,833, filed Jun. 24, 2005. Additional non-limitingexamples of probe card assemblies are illustrated in U.S. Pat. No.5,974,662 and U.S. Pat. No. 6,509,751 and the aforementioned U.S. patentapplication Ser. No. 11/165,833, filed Jun. 24, 2005, and variousfeatures of the probe card assemblies described in those patents andapplication can be implemented in the probe card assembly 100 show inFIG. 1.

DUT probes 106 can be arranged on substrate 116 into groups (referred toherein as DUT probe groups) in which each DUT probe group includes anumber and arrangement of probes for contacting the terminals 108 of oneDUT 110. A sufficient number of such DUT probe groups can be included onthe probe substrate 116 to contact and test a plurality of DUTs 110simultaneously. FIG. 2 depicts a portion of an example of one DUT probegroup 16, which can include a pattern of probes, like probes 18, 20.(Probes 18, 22 can be examples of probes 106.) The configuration in FIG.2 is exemplary of the many different types that can be used. In someembodiments, the probes in FIG. 2 can make up only a portion of theprobes in a DUT probe group 16. Each DUT probe group may include 60 to80 or more probes like those shown in FIG. 2, although in some instancesthere may be many fewer or many more. Because the wafer to be testedtypically includes DUTs 110 that are identical to one another, includingthe terminal 108 configuration on each DUT 110, the DUT probe groupsformed on substrate 116 can also be identical to one another. Each ofthe probes can include a tip, like tip 22 on probe 18 and tip 24 onprobe 20. As will be soon described, during wafer testing, probes in DUTprobe group 16 can be positioned opposite a wafer, similar to thedepiction of FIG. 1, and the wafer can be moved up toward the probes 106until the probe tips, like tips 22, 24 (in FIG. 2) contact correspondingterminals on the DUTs on the wafer.

The probes may be of any type, including needle probes, buckling beamprobes, bump probes, or spring probes. The probe bodies may beresilient, conductive structures. Non-limiting examples of suitableprobes include composite structures formed of a core wire that is overcoated with a resilient material as described in U.S. Pat. No.5,476,211, U.S. Pat. No. 5,917,707, and U.S. Pat. No. 6,336,269. Theprobes may alternatively be lithographically formed structures, such asthe spring elements disclosed in U.S. Pat. No. 5,994,152, U.S. Pat. No.6,033,935, U.S. Pat. No. 6,255,126, U.S. patent Application PublicationNo. 2001/0044225, and U.S. patent Application Publication No.2001/0012739. Other non-limiting examples of probes include thosedisclosed in U.S. Pat. No. 6,827,584, U.S. Pat. No. 6,640,432, and U.S.patent Publication No. 2001/0012739. Pogo pins, buckling beam probes(e.g., cobra probes), and other types of probes may also be used.

Similarly, regardless of probe type, the probe tip could be in the shapeof a pyramid, truncated pyramid, blade, bump, or any other suitableshape. Non-limiting examples of various shapes and sizes are describedin U.S. Pat. No. 6,441,315.

The probes that form DUT probe group 16 can be mounted on substrate 116.The substrate 116 can comprises a multi-layer ceramic substrate that caninclude a ground plane and a power plane connected to the appropriateprobes in the DUT probe groups, such as DUT probe group 16, on substrate116 for applying power to each DUT during testing. Substrate 116 may bea space transformer and/or can be made up of one or more tiles, eachcontaining a portion of the DUT probe groups, such as DUT probe group16. As discussed above, each of the probes in the DUT probe group 16 canbe connected via different electrical paths through the substrates 116,114, 112 to an individual channel connection in connectors 104 on awiring substrate 112. Alternatively or in addition, such electricalpaths can electrically connect one channel connection in the connectors104 to more than one probe 106.

As is known in the art, the electrical paths between the connectors 104and the probes 106 may be made via interposer 114 (in FIG. 1) disposedbetween space transformer 114 and wiring substrate 112. There may be afew, tens, scores, hundreds, or even thousands of such paths. Asmentioned and as will later be described in more detail, the connectors104 on wiring substrate 112 can include individual channel connectionsthat can be connected to communications channels (not shown) from atester (not shown). Connectors 104 can thus be used to connect theprobes 106 to communications channels (not shown) to and/or from atester (not shown).

The DUT configuration, including the number, layout, and signalassignments of the terminals 108 of the DUTs 110, on each wafer can varyas a result of a number of different factors, e.g., differentmanufacturers, different products, different wafer sizes, etc. As aresult, the number, pattern, and signal assignments of probes in DUTprobe groups on the probe substrate 116 are designed according to thewafer DUT pattern that results from these factors.

Turning first to FIG. 3, indicated generally at 30 is a probe head,which includes a probe group configuration 33 formed on substrate 116,in FIG. 1, with probes 106 comprising probes in probe groupconfiguration 33. Probe group configuration 33 can include a total of201 DUT probe groups, each of which is indicated by one of the squaresin FIG. 3. Embodiments of the invention may be implemented with fewer ormore probe groups; 201 is an exemplary number used only to describe thisnon-limiting example. As mentioned above, each DUT probe group in probegroup configuration 33 may be substantially identical to one another fortesting substantially identical DUTs on a semiconductor wafer. It shouldbe appreciated, however, that the present invention may be implementedto test singulated dies.

Turning to FIG. 4, the probe head 33 is shown superimposed over asemiconductor wafer, the perimeter of which is not shown, having aplurality of DUTs formed thereon, in a DUT pattern 32. Each of the DUTsin pattern 32 is indicated by a square of the same size as the squaresindicating the DUT probe groups on the probe head 30. A hatched lineindicates each of the DUT probe groups on the probe head 30. Thesignificance of the different directions of hatching on some of the DUTprobe groups will be explained shortly.

A bold line in FIGS. 4 and 5 defines the perimeter of the DUTs formed onthe semiconductor wafer, i.e., the perimeter of DUT pattern 32. Thereare a total of 290 DUTs in pattern 32 to be registered with one of the201 probe groups in probe group configuration 33 at least once duringtwo touchdowns of the probe group. But this embodiment is implementedwith a tester that has fewer than 201 channels, i.e., there are fewertester channels than there are probes in the probe groups. As will beseen, some of the tester channels can be routed to different DUT probegroups between the first and second touchdowns. As will be seen, thisallows testing of each of the 290 DUTs in irregularly shaped DUT pattern32 using a tester with fewer channels than there are probes in the DUTprobe groups. The number 290 of DUTs is exemplary only, and othernumbers of DUTs (e.g., more or fewer) can be tested in otherconfigurations.

Referring again to FIG. 1, as discussed above, the probe card assembly100 can be connected to a tester (e.g., to channels from the tester). Asalso generally discussed above, the tester can be programmed in a mannerknown in the art in combination with a wafer prober to move the waferunder test against selected one of the DUT probe groups, to apply testsignals and power to the DUTs, and to receive output signals from theDUTs. In an exemplary embodiment, the tester can have 150 channels,which can be organized into channel groups. Each of the channel groupscan correspond to a DUT probe group. For example, each channel group caninclude individual channels that correspond in number and signalassignments to individual probes in a DUT probe group. Thus, a channelgroup can include sufficient channels to provide, through a probe group,power and ground connections and signal input connections to a DUT, andthe channel group can also include sufficient channels to connect,through probes in the probe group, to the output terminals of the DUT.

As can be seen in FIG. 4, a number of the DUT probe groups can beregistered with a corresponding number of DUTs on the wafer. But many ofthe DUTs are not registered with a corresponding DUT probe group becausethere are fewer DUT probe groups than there are DUTs. In addition, someof the DUT probe groups, like DUT probe group 34 and several DUT probegroups 36, extend beyond DUT pattern 32 and thus are not opposite (andthus not in contact with) a DUT.

To operate the probe head 30 of FIG. 3 in a 150-channel tester, theprobe head 30 and the wafer can be positioned relative to one another asshown in FIG. 4 with probes on the DUT probe groups in DUT probe groupconfiguration 33 opposite corresponding terminals on some of DUTs inpattern 32. The 150 tester channels can then be routed to 150 of the DUTprobe groups in configuration 33, namely those in FIG. 4 that arehatched from lower left to upper right, like DUT probe group 31. Thisleaves a section 38 of DUT probe groups (shown hatched from upper leftto lower right), including DUT probe group 40, over a corresponding DUTin DUT pattern 32 but effectively disconnected from any tester channels.In addition, DUT probe group 34 and DUT probe groups 36 (both hatchedfrom upper left to lower right) are not opposite DUTs, i.e., they extendbeyond DUT pattern 32. Probe groups 34, 36 are also effectivelydisconnected. All of the disconnected DUT probe groups are shown hatchedfrom upper left to lower right. Exemplary manners of connecting anddisconnecting the DUT probe groups to tester channels will be describedshortly.

After effectively disconnecting and connecting the DUT probe groups inconfiguration 33 as shown in FIG. 4 and discussed above, the wafer andthe probes can be moved relative to one another until the probes makecontact with terminals on the DUTs. Alternatively, the wafer and theprobes can be moved relative to one another to make contact betweenprobes and DUT terminals, and thereafter DUT probe groups inconfiguration 33 can be disconnected and connected as described above.Regardless of whether the disconnecting and connecting occurs before orafter contact between the probes and DUT terminals is effected, oncecontact is effected, DUTs can be supplied with power from theappropriate probes in the DUT probe groups in configuration 33 that arehatched from lower left to upper right, and a predetermined test ortests can be simultaneously run on each of the DUTs in pattern 32 thatis opposite a connected DUT probe group. Various input signals can besupplied to the DUT, and DUT outputs can be monitored to determinewhether the DUT is functioning as designed. After the test or tests arerun and a determination is made as to which DUTs pass the testing andwhich do not, the probe head and the wafer can be separated from oneanother, and the probe head can be stepped, e.g., moved laterallyrelative to the wafer, to the position of FIG. 5.

Before the second touchdown, which is depicted in FIG. 5, some of thetester channels can be switched to a different set of DUT probe groups,namely some of those that were effectively disconnected in the firsttouchdown. Like FIG. 4, those DUT probe groups that are effectivelydisconnected from tester channels are shown hatched from upper left tolower right in FIG. 5, namely the DUT probe groups in sections 41, 42.And those that are effectively connected to a tester channel are hatchedfrom lower left to upper right.

It should be appreciated that embodiments can be implemented in whichthe tester channels are switched and additional testing of previouslyuntested DUTs is performed during the first touchdown. Alternatively,the switching may occur during the first touchdown and the probe headand wafer separated and stepped without further testing during the firsttouchdown.

In FIG. 5, 150 channels are each connected to a DUT probe group asdepicted by the hatching and described above. Probe group 30 and thewafer are then again moved into contact with one another so that theprobes make pressure connections against corresponding terminals on theDUTs. There are a few DUTs, e.g., DUT 44, that are subject to twotouchdowns by effectively connected DUT probe groups, one in FIG. 4 anda different one in FIG. 5. These DUTs, like DUT 44, need not be testedtwice. They can be dealt with by programming the tester not to retestsuch DUTs during the second touchdown. Alternatively, the tester canretest such DUTs during the second touchdown in the same manner as theDUTs were tested during the first touch down. This can leave fewer than150 channels connected during the second touchdown but still tests allthe DUTs without testing any twice. After the second touchdown, powercan again be applied to the DUTs and the same tests can be run therebytesting the remaining DUTs.

Another embodiment of the invention is depicted in FIGS. 6 and 7.Indicated generally at 610 is a probe head that includes a DUT probegroup configuration 612. Probe group configuration 612 includes aplurality of DUT probe groups that are depicted schematically bysquares, two of which are DUT probe groups 614, 616. The DUT probegroups can be mounted on a substrate, which in the exemplary embodimentof FIGS. 6 and 7, comprises a substrate 618 (e.g., like substrate 116 ofFIG. 1), which can be part of a probe card assembly (e.g., like probecard assembly 100 of FIG. 1). As mentioned above, each DUT probe groupin probe group configuration 612 may be substantially identical to oneanother for testing substantially identical DUTs on a semiconductorwafer. It should be appreciated, however, that the present invention maybe implemented to test singulated dies or other types of DUTs.

Probe head 610 is shown superimposed over a semiconductor wafer, theperimeter of which is not shown, having a plurality of DUTs formedthereon in a DUT pattern 620, which is the same DUT pattern depicted inFIGS. 4 and 5. A line defines the perimeter of DUT pattern 620—boldwhere not obscured and dashed when DUT pattern 620 is covered by probehead 612. Each of the DUTs in DUT pattern 620 is indicated by a squareof the same size as the squares indicating the DUT probe groups, such asDUT probe groups 614, 616, on probe head 610. A bold line in FIGS. 6 and7 defines the perimeter of the DUTs in DUT pattern 620 formed on thesemiconductor wafer. A hatched line indicates each of the DUT probegroups, including DUT probe groups 614, 616, on probe head 610. Thesignificance of the different directions of hatching on some of the DUTprobe groups is the same as FIGS. 4 and 5, i.e. hatching from upper leftto lower right indicates an effectively disconnected probe group, andhatching from lower left to upper right indicates an effectivelyconnected DUT probe group. Probe head 610 can be connected to a tester(not shown) in a manner similar to that described for probe head 30. Thetester (not shown) can include fewer tester channels than there are DUTprobe groups—two of which being DUT probe groups 614, 616—on the probehead.

As a result, some of the tester channels can be routed to different DUTprobe groups between the first touchdown, depicted in FIG. 6, and thesecond touchdown, depicted in FIG. 7. As will be seen, this can allowtesting of each of the DUTs in irregularly shaped DUT pattern 620 usinga tester with fewer channels than there are probes in the DUT probegroups.

When probe head 610 is incorporated into a probe card assembly, e.g., inthe same manner probe substrate 116 is incorporated into probe cardassembly 100 in FIG. 1, the probe head 610 can be connected to a tester(not shown). The tester can be programmed in a manner known in the artin combination with a wafer prober (not shown) to move the wafer undertest against selected ones of the probe groups, such as DUT probe groups614, 616; to apply test signals and power to the DUTs in selected onesof the DUTs in DUT pattern 620; and to receive output signals from thoseDUTs.

As can be seen in FIG. 6, a number of the DUT probe groups, one of whichis DUT probe group 614, can be registered with a corresponding DUT inDUT pattern 620. But many of the DUTs, e.g., those on the right side ofthe DUT pattern 620, are not registered with a corresponding DUT probegroup because there are fewer DUT probe groups in DUT probe groupconfiguration 612 than there are DUTs in DUT pattern 620. In addition,some of the DUT probe groups, e.g., DUT probe 616, extend beyond DUTpattern 620 and thus are not opposite a DUT.

To operate probe head 610 to test DUTs in DUT pattern 620, probe head610 and the semiconductor wafer on which DUT pattern 620 is formed canbe positioned relative to one another as shown in FIG. 6 with probes onthe DUT probe groups, such as DUT probe group 614, being oppositecorresponding terminals on some of the DUTs in DUT pattern 620. As canbe seen in FIG. 6, DUT probe group 614 is over a corresponding DUT onDUT pattern 620 while DUT probe group 616 is not over a correspondingDUT. In fact, it may not be over any part of the wafer on which DUTpattern 620 is formed or it may be over a part of the wafer that doesnot include DUT pattern 620. All of the DUTs on the left side of DUTpattern 620 are opposite a corresponding DUT probe group, such as DUTprobe group 614.

While probe head 610 and DUT pattern 620 are positioned relative to oneanother as shown in FIG. 6, tester channels can be connected to probesin ones of the DUT probe groups—such as probe group 614—that are acrossfrom a corresponding DUT, namely those in FIG. 6 that are hatched fromlower left to upper right, like DUT probe group 614. This leaves anumber of DUT probe groups (shown hatched from upper left to lowerright), like DUT probe group 616, effectively disconnected from anytester channels. Exemplary manners of connecting and disconnecting theDUT probe groups to tester channels will be described shortly.

After effectively disconnecting and connecting the DUT probe groups inDUT probe group configuration 612 as shown in FIG. 6, the wafer (notshown) and the probes can be moved relative to one another until theprobes make contact with terminals on the DUTs. Again, however, thedisconnecting and connecting can occur after effecting contact betweenthe probes and terminals on the DUTs. Regardless of whether thedisconnecting and connecting occurs before or after effecting contact,once contact has been effected between probes and DUT terminals, eachDUT can be supplied with power from the appropriate probes in DUT probegroup configuration 612 that are hatched from lower left to upper right,and a predetermined test or tests can be simultaneously run on each ofthe DUTs in DUT pattern 620 that is opposite a connected DUT probegroup. Various input signals can be supplied to each DUT, and DUToutputs can be monitored to confirm that the DUT is functioning asdesigned. After the test or tests run and a determination is made as towhich DUTs pass and which do not, probe head 610 and the wafer can beseparated from one another, and the probe head can be stepped, e.g.,moved laterally relative to the wafer, to the position of FIG. 7.

Before the second touchdown, which is depicted in FIG. 7, some of thetester channels can be switched to a different set of DUTs, namely someof those that were effectively disconnected in the first touchdown.Alternatively, switching of the tester channels can occur after thesecond touchdown. Like FIG. 6, those DUTs that are effectivelydisconnected are shown hatched from upper left to lower right in FIG. 7,such as DUT probe group 614, and those that are effectively connected toa tester channel are hatched from lower left to upper right, such as DUTprobe group 616.

It should be appreciated that the invention may be implemented inembodiments in which the tester channels are switched and additionaltesting of previously untested DUTs is performed during the firsttouchdown. Alternatively, the switching may occur during the firsttouchdown and the probe head and wafer separated and stepped withoutfurther testing during the first touchdown. Also, the probe head maymove in any direction and cover different numbers of DUTs in eachtouchdown.

In FIG. 7, channels are each connected to probes of ones of the DUTprobe group as depicted by the hatching. DUT probe group configuration612 and some of the DUTs in DUT pattern 620 are then moved into contactwith one another so that probes make a pressure connection againstcorresponding terminals on the DUTs. After the second touchdown, powercan again be applied to the DUTs and the same test or tests can be runthereby testing the remaining DUTs. As a result, each of the DUTs in DUTpattern 620 can be touched and tested using a tester that has fewerchannels than the number of DUT probe groups.

Turning now to FIG. 8, indicated generally at 46 is a portion of acircuit constructed in accordance with some embodiments of the presentinvention. As will be discussed, the circuit shown in FIG. 8 can beimplemented in whole or in part on a probe card assembly like the probecard assembly 100 of FIG. 1.

As shown in FIG. 8, circuit 46 can include a signal line 51, which canbe electrically connected to a source of test signals. For example,signal line 51 can be electrically connected to a channel connection inelectrical connectors 104 of FIG. 1. As such, signal line 51 can be partof an electrically conductive path (e.g., a first path) betweenelectrical connectors 104 and probes 106 of FIG. 1. Exemplaryimplementations of such paths are discussed above with respect toFIG. 1. As shown in FIG. 1, the signal line 51 can be electricallyconnected to a plurality of probes (e.g., a first set of probes) throughpotentiometers. As also shown, the probes can be brought into contactwith or otherwise form electrical connections with input and/or outputterminals of DUTs. Three probes, three potentiometers, and three DUTsare shown in FIG. 8 but signal line 51 can be connected to more or fewerprobes through more or fewer potentiometers, and the probes can contactmore or fewer DUTs. Two of the probes are labeled 52, 54 in FIG. 8, twoof the potentiometers are labeled 47, 48 in FIG. 8, and two of the DUTsare labeled 56, 58 in FIG. 8. Hereinafter, reference to potentiometers47, 48 can include any or all of the potentiometers shown in FIG. 8.Likewise, reference to probes 52, 54 and DUTs 56, 58 can include any orall of the probes shown in FIG. 8 and any or all of the DUTs shown inFIG. 8, respectively. The probes 52, 54 shown in FIG. 8 can be likeprobes 106 of FIG. 1 and can be configured to contact input and/oroutput terminals (not shown in FIG. 8) of the DUTs 56, 58, each of whichcan be like DUT 110 with terminals 108 in FIG. 1.

A plurality of circuits like circuit 46 can be provided on the probecard assembly 100. For example, such additional circuits can connectother signal lines (which can be like signal line 51) to other channelconnections in electrical connectors 104 (see FIG. 1). Such additionalsignal lines can also be connected through potentiometers likepotentiometers 47, 48 to probes like probes 52, 54. Some such additionalprobes can contact the DUTs 56, 58 shown in FIG. 8 and thus, with theprobes 52, 54 shown in FIG. 8, can form DUT probe groups (e.g., like DUTprobe group 16 or any other DUT probe group disclosed herein) forcontacting all or many of the terminals of the DUTs 56, 58. Others ofthe additional probes can contact other DUTs (not shown in FIG. 8.)

As shown in FIG. 8, each potentiometer can include a control input. InFIG. 8, control signals to the control inputs of each potentiometer 56,58 are shown as provided from a multiplexer 50, although in otherembodiments, such control signals can be provided through or from othercircuit elements or electronic entities. In some embodiments, eachcontrol signal provided to each control input of a potentiometer 47, 48can have two states. A first state of the control signal can cause theimpedance level of the potentiometer 47, 48 to which the control signalis applied to have a sufficiently high impedance so as not to passsignals (e.g., test signals from a tester) received on signal line 51. Asecond state of the control signal can cause the potentiometer 47, 48 tohave a sufficiently low impedance to pass signals (e.g., test signalsfrom a tester) received on signal line 51. Control signals in differentstates can be selectively applied to the potentiometers to put eachpotentiometer in either the high impedance state or the low impedancestate. In this manner, any pattern of the probes 52, 54 shown in FIG. 8can be selected to pass and block signals received on signal line 51.All other instances of circuit 46 implemented on the probe card assembly100 (see FIG. 1) can similarly be configured to select particularpatterns of probes through which to pass signals received from a signalsource (e.g., a tester).

Multiplexer 50 with input 50a, bus 57, microprocessor 55, and memory 59in FIG. 8 illustrate an exemplary circuit for controlling application ofcontrol signals to the control inputs of the potentiometers 52, 54. Oneor more control signals and/or inputs applied to the multiplexer 50 atinput 50 a can cause the multiplexer 50 to output different patterns ofcontrol signals to the potentiometers 52, 54, which as discussed above,can selectively place some of the potentiometers into a high impedancestate and some into a low impedance state. As also shown, amicroprocessor 55 operating under control of software (e.g., software,firmware, microcode, or any other form of programmed instructions)stored in a memory 59 can provide the control and/or input signalsthrough a bus 57 to the multiplexer 50.

All or part of the circuit formed by the multiplexer 50, bus 57,microprocessor 55, and memory 59 can be located on the probe cardassembly 100 (see FIG. 1). For example, the multiplexer 50, bus 57,microprocessor 55, and memory 59 can be located on the probe cardassembly 100. As another example, the multiplexer 50 can be located onthe probe card assembly 100, and the memory 59 and microprocessor 55 canbe located in a tester (not shown). In such an implementation, the bus57 can comprise channels from the tester and electrical paths throughthe probe card assembly 100 from channel connections in electricalconnectors 104 to the multiplexer 50. As yet another example, themultiplexer 50, bus 57, microprocessor 55, and memory 59 can be locatedat the tester (not shown), and outputs of the multiplexer 50 can beprovided to the probe card assembly 100 through channels from the testerthat connect to channel connections in the electrical connectors 104 ofthe probe card assembly 100 (see FIG. 1).

The control circuitry comprising multiplexer 50, bus 57, microprocessor55, and memory 59 is exemplary only, and other means can be used toprovide control signals to the control inputs of the potentiometers 52,54. For example, microprocessor 55 can be replaced in whole or in partby hardwired logic circuitry. As another example, multiplexer 50 neednot be included, and microprocessor 55 can provide control signalsdirectly to the potentiometers 52, 54 or through circuit elements otherthan a multiplexer (e.g., buffers). As still another example of apossible modification, all or part of the control circuitry representedby multiplexer 50, bus 57, microprocessor 55, and memory 59 can belocated other than on the probe card assembly 100 or in a tester (notshown) to which the probe card assembly 100 is connected. For exampleall or part of that circuitry can be located in a device (other than atester) that can be electrically connected to the probe card assembly100.

Consistent with the discussion above, for the sake of clarity in thedrawings, only a single probe is shown for each DUT probe group that isconnected to each DUT 56, 58 in FIG. 8. In the usual case there are, ofcourse, a number of probes from each DUT probe group connected toterminals on each DUT 56, 58, each probe having a corresponding digitalpotentiometer connection as shown in FIG. 8. In addition, in theexemplary embodiment, a total of 102 DUT probe groups are wired inparallel as show in FIG. 8. As will be seen, this permits switchingbetween two different groups of 51 DUT probe groups. As with previouslydescribed embodiments, numbers of DUT probe groups may be used that aremore or greater than the 102 used in this example. And the two differentgroups of DUT probe groups may be equal in number and be greater or lessthan 51 DUT probe groups or they may have differing numbers of DUT probegroups in each group.

Considering now the operation of the circuit of FIG. 8, processor 55 canbe programmed in a known manner to apply control signals, viamultiplexer 50, to each potentiometer 47, 48. The control signals canhave two states. As discussed, a first state of the control signal cancause the impedance level of the potentiometer or potentiometers towhich the control signal or signals are applied to have a sufficientlyhigh impedance so as not to pass signals (e.g., test signals from atester) received on signal line 51. A second state of the control signalcan cause a potentiometer to have a sufficiently low impedance to passsignals (e.g., test signals from a tester) received on signal line 51.Control signals in different states can be selectively applied to thepotentiometers to put each potentiometer in either the high impedancestate or the low impedance state. This functionality can be used tocreate a first predetermined pattern of DUT probe groups that areoperational for testing, as shown in FIG. 4. After the operational probegroups and corresponding DUTs are moved relative to one another to bringthe probes into pressure contact with the DUTs, as shown in FIG. 4,testing proceeds in a known manner, and the probes are removed. Thecircuit depicted in FIG. 8 can then used to create a secondpredetermined pattern of operational DUT probe groups, as shown in FIG.5. The probes are again brought into contact with the wafer and testingagain proceeds.

Turning now to FIG. 9, in another embodiment, structure that correspondsto previously described structure is identified with the same numeral.The circuit of FIG. 9 includes resistors 60, 62, each in parallel with aswitch 64, 66. Although three resistors and switches are shown and tworesistors are labeled 60, 62 and two switches 64, 66 are labeled in FIG.9, more or fewer resistors and switches can be used, and referencesherein to resistors 60, 62 or switches 64, 66 refers to some or al ofthe resistors or switches, respectively, in FIG. 9. In the configurationshown in FIG. 9, each resistor 60, 62 and its associated switch 60, 62,in essence, takes the place of a potentiometer in the configurationshown in FIG. 8. The impedance values of the resistors 60, 62 can besufficiently high to effectively prevent signals received on signal line51 from passing, and a switch 64, 66, while closed, can provide a lowimpedance by-pass electrical path by-passing its associated resistorwhile closed and thus allowing signals received on signal line 51 topass to the associated probe 52, 54. The configuration shown in FIG. 9can otherwise be like and can be configured and operated like theconfiguration shown in FIG. 8.

Switches 64, 66 may be mechanical, such as relay contacts, or may besolid-state switches. The opening and closing of the switches can beunder control of the programmed processor 55 or can be controlled usingany the alternatives discussed above with respect to FIG. 8. Asmentioned, the FIG. 9 embodiment can function like the FIG. 8 embodimentexcept that opening and closing of the switches 64, 66 is used toeffectively connect, when a switch is closed, and disconnect, when aswitch is open, each probe 52, 54 to signal line 51. For example, theimpedance value of the resistors (e.g., 60, 62) can be sufficiently highto effectively prevent signals (e.g., test signals from a tester towhich signal line 51 is connected) received on signal line 51 frompassing through the resistor.

FIG. 10 illustrates an embodiment that can be generally similar to theembodiments of FIGS. 8 and 9 except a chip select terminals can beprovided on each DUT 56, 58. The chip select terminal of a particularDUT can be configured to selectively connect and disconnect circuitryinternal to the particular DUT to or from input and/or output terminals(not shown in FIG. 10) of the particular DUT. Each DUT 56, 58 in FIG. 10is shown with a chip select terminal 70, 72.

In the embodiment of FIG. 10, a chip select controller 68 can operateunder control of the programmed processor 55 or under control of any ofthe control variations described above with respect to FIG. 8. A chipselect controller 68 can be on a probe card assembly like probe cardassembly 100 of FIG. 1. Programmed processor 55 can also be on such aprobe card assembly 100 or in a tester. This embodiment relies onappropriate DUTs formed on the wafer to have a chip select (CS) terminal70, 72. During testing, probes, like probe 73, can contact the CSterminal 70, 72 of the DUTs 56, 58, and the selector 68 can control thestate of the signal applied to the CS terminal 70, 72 of each of theDUTs 56, 58. The chip select terminals 70, 72 may be designed into theDUTs with the intention of facilitating the testing process or may bepart of the DUT design that was contemplated in the finished device.

In any event, referring to DUT 58, while the chip select terminal 72 isin a first state responsive to a voltage appearing on probe 73, theinput and/or output terminals (not shown in FIG. 10 but which can belike terminals 108 of FIG. 1) of DUT 58 are coupled (e.g., electricallyconnected) to the internal circuitry of DUT 58, which means that DUT 58is connected to signal line 51 through probe 54. When, however, the chipselect terminal 72 is in a second state, the DUT 58 internal circuitryis uncoupled from the input and/or output terminals of the DUT 58. Inthis state, although probe 54 is electrically connected to the inputand/or output terminals of DUT 58, test signals on signal line 51 arenot input into the DUT 58. This is accomplished in a known manner, e.g.,by placing at least some of the DUT terminals in high impedance orfloating state in response to application of the second state to thechip select terminal. The chip select terminals on the other DUTs inFIG. 10 can operate like the chip select terminal 72.

The resistors shown in FIG. 10 connected to probes 52, 54 are optional.They may be used to provide some isolation between DUTs 56, 58 duringtesting. Thus, the resistors can be sized with a sufficiently lowimpedance to allow test signals to pass but with a sufficiently highimpedance to isolate one probe from a fault at a DUT with which anotherof the probes is in contact.

The embodiment of FIG. 10 can operate as described above with theprogrammed chip selection occurring to create the patterns of FIGS. 4and 5 during the testing process. It should be appreciated that in anyof the embodiments, switching between the predetermined patterns ofFIGS. 4 and 5 can occur without removing the probes from the DUTterminals. In addition, more than two patterns can be created duringtesting and different numbers of DUT probe groups can be made intopatterns of any shape. Any of these embodiments can be effectivelyimplemented in a probe group like that shown in co-pending U.S. patentapplication Ser. No. 11/028,940 for Probe Head Arrays, which is alsoassigned to the assignee of this application. The invention can also beimplemented with any other type of probe card, such as a needle card,cobra card, a membrane card, or any other suitable probe card.

The embodiment of FIG. 11 is similar to that of FIG. 10 except that inFIG. 11, a single tester channel (e.g., connected to one of signal lines76, 78, 80) may drive more than one input to one or more DUT probes 90,92 during a single test. Signal lines 76, 78, 80 can be generallysimilar to and can be configured and electrically connected to a channelconnection in the electrical connectors 104 of the probe card assembly100 of FIG. 1 as discussed above with respect to FIG. 8. A non-limitingexample of driving multiple probes is disclosed in U.S. Pat. No.6,452,411. As can be seen in an exemplary embodiment of FIG. 11, aplurality of lines 76, 78, 80 can be connected to differentcommunications channels from a tester (not shown). For example, each oflines 76, 78, 80 can be part of a probe card assembly, like probe cardassembly 100 of FIG. 1, and can be connected by one of the electricallyconductive paths discussed above with respect to FIG. 1 to a channelconnection in the electrical connectors 104. Each of lines 76, 78, 80can be connected to isolation resistors, like line 80 is connected toisolation resistors 86, 88. The isolation resistors in FIG. 11 can belike and can be sized like the resistors of FIG. 10. The other sides ofresistors 86, 88 can be connected to probes 90, 92, each being in adifferent DUT probe group but connected to a single tester channel vialine 80. In the FIG. 11 embodiment, probes 90, 92 are shown pressureconnected to terminals on DUTs 80, 84, respectively. As with FIG. 10,all of the probes associated with each DUT probe group are not shown tosimplify the drawing. It will be appreciated that each DUT probe group,e.g., the DUT probe group that is pressure connected to DUT 84, can havenumerous probes, each ultimately connected to channel connection in theelectrical connectors 104 of FIG. 1. Like the FIG. 10 embodiment, eachof the chip select CS terminals on the DUTs, like the CS terminal on DUT84, can be connected to a selector 90 (which can be like 68 of FIG. 10)via probes that are pressure connected to each of the chip select CSterminals.

Operation of the embodiment of FIG. 11 can be similar to that of FIG. 10The chip select signals can be set to permit simultaneous testing of twoDUTs by a single tester channel. Alternatively, the chip select signalscould be selected so that only one DUT is operative for testing in eachchannel during a single test. Or some DUTs could be selected forsimultaneous testing by a single channel by applying the appropriatesignal on each of the CS terminals in that channel while other DUTs mayhave one DUT selected and one DUT not in a single channel. Thisflexibility provides for multiple ways in which different patterns, suchas those shown in FIGS. 4 and 5 and in FIGS. 6 and 7, during differenttouchdowns may be selected for testing to optimize a test procedure.

1. A contactor device comprising: an electrical interface to a pluralityof communications channels from a tester; a plurality of electricallyconductive probes disposed to contact electronic devices to be tested;electrically conductive paths electrically connecting the electricalinterface and ones of the probes, a first one of the electrical pathselectrically connecting a first one of the communications channels to afirst set of more than one of the probes; and means for selecting fewerthan all of the probes in the first set of probes through which toprovide test signals from the first communication channel to at leastone of the electronic devices.
 2. The probe card assembly of claim 1,wherein: the first set of probes comprises at least three probes, andthe means for selecting is configured to select as a first combinationany combination of fewer than all of the probes in the first set ofprobes through which to provide the test signals.
 3. The probe cardassembly of claim 1, wherein the means for selecting comprises aplurality of potentiometers each disposed in the first electrical pathbetween the electrical interface and one of the probes of the first setof probes.
 4. The probe card assembly of claim 3, wherein each of thepotentiometers comprises a control input that controls an amount ofimpedance of the potentiometer.
 5. The contactor device of claim 4,wherein: while the control input is in a first state, the impedance ofthe potentiometer is sufficiently high to effectively prevent testsignals from passing through the potentiometer, and while the controlinput is in a second state, the impedance of the potentiometer issufficiently low to effectively allow test signals to pass through thepotentiometer.
 6. The probe card assembly of claim 1 further comprisinga plurality of resistors each disposed in the first electrical pathbetween the electrical interface and one of the probes of the first setof probes.
 7. The probe card assembly of claim 6, wherein the means forselecting comprises a plurality of by-pass switches each configured to,while closed, provide an electrical path by passing one of theresistors.
 8. The contactor device of claim 7, wherein the impedancelevel of each of the resistors is sufficiently high to effectivelyprevent test signals from passing through the resistor.
 9. The probecard assembly of claim 8, wherein each of the switches comprises acontrol input that controls whether the switch is open or closed. 10.The probe card assembly of claim 1, wherein the probes in the first setof probes are configured to contact a first set of the electronicdevices, and the means for selecting comprises a second plurality ofprobes each configured to contact an enable input on one of the firstset of electronic devices.
 11. The contactor device of claim 1, whereinthe contactor device comprises a probe card assembly.
 12. An apparatusfor testing a plurality of semiconductor devices comprising: a chipselect port on at least one of the devices that couples contacts on thedevice to internal circuits within the device in response to a firststate on the port and that uncouples contacts on the device from theinternal circuits in response to a second state on the port; a pluralityof groups of test probes, each group of test probes configured tocontact one of the devices; a tester having a plurality of groups oftester channels, each group of tester channels configured to correspondto one of the groups of test probes, wherein a number of the groups oftester channels is less than a number of the groups of test probes, andat least one of the groups of tester channels is connected to more thanone of the groups of test probes via conductors disposed between thetester channels and the test probes; and a processor programmed toselectively apply the first and second states to the chip select portduring testing of the devices.
 13. The apparatus of claim 12, whereinthe processor is programmed to connect a first predetermined pattern ofthe groups of test probes to the groups of tester channels during afirst touchdown of ones of the probes onto contacts of a first group ofthe devices and to connect a second predetermined pattern of the groupsof test probes to the groups of tester channels during a secondtouchdown of ones of the probes onto contacts of a second group of thedevices.
 14. The apparatus of claim 13, wherein said first and secondpredetermined patterns are different from one another.
 15. The apparatusof claim 12, wherein when the groups of test probes touch contacts oncorresponding devices and said first state is asserted, the one deviceis effectively connected to a first of the groups of tester channels.16. The apparatus of claim 12, wherein when the groups of test probestouch contacts on corresponding devices and said second state isasserted, the one device is effectively disconnected from the first ofthe groups of tester channels.
 17. The apparatus of claim 12, whereinthe groups of test probes part of a probe card assembly.
 18. Theapparatus of claim 12, wherein the devices are formed on a semiconductorwafer.
 19. A method for testing at least a first and a second group ofDUTs using a contactor device having a plurality of groups of testprobes, the method comprising: connecting a group of tester channels tomore than one of the groups of test probes via conductors disposedbetween the tester channels and the probes; bringing ones of the groupsof test probes and contacts of the first group of DUTs into contact;asserting a first state at a chip select port on at least one of theDUTs in the first group of DUTs; testing ones of the first group ofDUTs; bringing ones of the groups of test probes and contacts of thesecond group of DUTs into contact; asserting a second state at the chipselect port on the at least one of the DUTs in the first group of DUTs;and testing ones of the second group of DUTs.
 20. The method of claim19, wherein there are fewer tester channels than there are probes in thegroups of test probes.
 21. The method of claim 19, wherein the first andsecond groups of DUTs form different patterns.
 22. The method of claim19, wherein the probes of the probe groups are part of a probe cardassembly.
 23. The method of claim 19, wherein asserting a state at achip select port on the at least one of the DUTs comprises applying thestate to one of the contacts on the at least one DUT via one of theprobes in the groups of test probes.
 24. The method of claim 19, whereinthe DUTs are formed on a semiconductor wafer.
 25. The method of claim19, wherein the at least one of the DUTs in the first group of DUTs isalso in the second group of DUTs.
 26. The method of claim 19, whereinthe chip select port selectively enables the at least one of the DUTs toreceive input signals and disables the at least one of the DUTs fromreceiving input signals.
 27. A method for testing at least a first and asecond group of DUTs using a contactor device having a plurality ofgroups of test probes, the method comprising: connecting at least one ofa group of tester channels to more than one group of test probes viaconductors disposed between the tester channel and the probes; disposingvariable resistive elements in at least some of the conductors; bringingones of the groups of test probes and contacts of the first group ofDUTs into contact; selectively setting a resistive state of at least oneof the variable resistive elements to one of a first state or a secondstate, wherein in the first state, each variable resistive elementeffectively prevents test signals from passing through the variableresistive element, and in the second state, the variable resistiveelement allows test signals to pass through the variable resistiveelement. testing ones of the first group of DUTs; bringing ones of thegroups of test probes and contacts of the second group of DUTs intocontact; changing a state of at least one of the variable resistiveelements after testing the first group of DUTs; and testing ones of thesecond group of DUTs.
 28. The method of claim 27, wherein, in the firststate, the variable resistive elements have a first impedance level, andin the second state, the variable resistive elements have a secondimpedance level, and the first impedance level is higher than the secondimpedance level.
 29. The method of claim 28, wherein the first impedancelevel is at least five times the second impedance level.
 30. The methodof claim 27, wherein each of ones of the variable resistive elementscomprises a potentiometer.
 31. The method of claim 30, wherein settingthe first state of one of the ones of the variable resistive elementscomprises maintaining the potentiometer at a high impedance level, andsetting the second state of each of one of the ones of the variableresistive elements comprises maintaining the potentiometer at a lowimpedance value.
 32. The method of claim 27, wherein each of thevariable resistive elements comprises a resistive element in parallelwith a switch.
 33. The method of claim 32, wherein setting one of thevariable resistive elements to the first state comprises maintaining theswitch in an open condition, and setting one of the variable resistiveelements to the second state comprises maintaining the switch in aclosed condition.
 34. The method of claim 27, wherein there are fewertester channels than there are probes.
 35. The method of claim 27,wherein the selectively setting a resistive state of at least one of thevariable resistive elements to one of a first state or a second state isperformed prior to the bringing ones of the groups of test probes andcontacts of the first group of DUTs into contact, and the changing astate of at least one of the variable resistive elements after testingthe first group of DUTs is performed prior to the testing the ones ofthe second group of DUTs.
 36. The method of claim 27, wherein theselectively setting a resistive state of at least one of the variableresistive elements to one of a first state or a second state isperformed after the bringing ones of the groups of test probes andcontacts of the first group of DUTs into contact.
 37. The method ofclaim 27, wherein the first and second groups of DUTs form differentpatterns.
 38. The method of claim 27, wherein the DUTs are formed on asemiconductor wafer.
 39. The method of claim 27, wherein the contactordevice comprises a probe card assembly.
 40. The method of claim 27,wherein the first group of DUTs and the second group of DUTs have atleast one common DUT.